EP1167917A1 - Method for wall thickness measurement of a hollow blade - Google Patents

Method for wall thickness measurement of a hollow blade Download PDF

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Publication number
EP1167917A1
EP1167917A1 EP01401719A EP01401719A EP1167917A1 EP 1167917 A1 EP1167917 A1 EP 1167917A1 EP 01401719 A EP01401719 A EP 01401719A EP 01401719 A EP01401719 A EP 01401719A EP 1167917 A1 EP1167917 A1 EP 1167917A1
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European Patent Office
Prior art keywords
wall
detector
partitions
thickness
signal
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German (de)
French (fr)
Inventor
Franck Paul Dominique Panizzoli
Dominique Marc Bruno Placko
Eduardo Agapito Santander-Rojas
Yann Le Bihan
Olivier Lespinet
Alain Mourenko
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Safran Aircraft Engines SAS
Centre National de la Recherche Scientifique CNRS
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Centre National de la Recherche Scientifique CNRS
SNECMA Moteurs SA
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Publication of EP1167917A1 publication Critical patent/EP1167917A1/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
    • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
    • G01N27/9073—Recording measured data
    • G01N27/9086—Calibrating of recording device
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
    • G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance

Definitions

  • the subject of this invention is measurement thickness of a wall of a hollow blade.
  • a feature of these pieces is that they are normally fitted with internal partitions covered by the wall, in order to stiffen the dawn or to compartmentalize the internal volume. These partitions disturb the measurements since their contributions to measurement signal overlap those of the wall and that they therefore tend to be confused with extra thickness.
  • ultrasonic measurements are not suitable for everyone materials, especially those that are anisotropic.
  • the process is based on the use of a particular eddy current detector, which is designed and used so that the contribution of partitions to the signal collected is minimized, and means of treatment are offered to eliminate substantially the influence of partitions on the measured.
  • a particular eddy current detector which is designed and used so that the contribution of partitions to the signal collected is minimized, and means of treatment are offered to eliminate substantially the influence of partitions on the measured.
  • the invention relates to a method for measuring the thickness of a wall hollow blade capable of covering partitions, characterized in that it consists in applying two poles of a magnetic core of a current detector Eddy on the wall in alignment parallel to partitions, the poles (8) being provided with coils (7) connected together in series, to move the detector on the wall perpendicular to the partitions, at record a signal produced by the detector, and deduce the wall thickness from calibrations preliminary.
  • Figure 1 partially shows a 1 hollow blade whose profile is drawn by a wall exterior 2 stiffened by partitions 3 of widths, of different and poorly known depths and gaps.
  • a sensor 4 is moved along a generator 5 of dawn 1. It comprises a magnetic core 6 in a hoop, on which an electromagnetic coil is formed, here composed of two coils 7 connected together in series and placed on the branches 8 of the hoop 6.
  • the detector 4 is at the end of a support arm 9 pushed back by a spring 10 so that the ends of the branches 8 touch the wall 2; a motorized device 11 allows to move the arm 9 and the detector 4 along the generator 5.
  • An alternating current generator 12 is placed on an electrical circuit 13 to which the coils 7 are connected in series, and a voltmeter 14 saves the voltage produced across the coils 7 and transmit it to a processing means 15 which constitutes an important element of the invention.
  • the signal measured by the voltmeter 14 depends in particular of the eddy currents that induction electromagnetic coil 7 produced on the portion near dawn 1, and which depends, in addition to the thickness of the wall 22, the presence or the absence of a partition 3 in front of the detector 4 or at proximity.
  • the influence of partitions 3 becomes almost imperceptible, so that we can even conceive of completely ignoring their existence and directly deducing the thickness of wall 2 from the signal received, after a preliminary calibration carried out on a series of smooth walls of different thickness.
  • the input data circulates in the network being modified with each neuron that they cross.
  • the neurons can be divided into successive layers and linked to all the neurons of the previous layer and the next layer.
  • a two-layer network comprising an output layer C 2 with a single neuron providing the desired output (the thickness) and with a lower or hidden layer C 1 composed of a few neurons (two, three or four in practice) supplied by the values obtained from the signal (R 1 or R 2 for example) was sufficient.
  • the neural network undergoes a prior learning which then allows it to express the descriptive parameters of a new situation, resembling the learning situation, according to the signals it receives. It is proposed here to make a calibration by means of a flat shim 30 (FIG. 6) formed of parallel strips 31 of increasing thickness and provided with ribs 32, similar to partitions 3, behind this plate, at different intervals, possibly d 'different thicknesses and widths which cut all the bands 31.
  • the detector 4 is walked along these bands 31 in the same way as for blade 1, so that it provides a sufficient number of reference signals which are exploited to regulate the neural network by adjusting the weights and their biases.
  • Such learning of the neural network can be done automatically by software so that the network outputs the known thickness of each band 31 as a function of the signals picked up by traversing this band.
  • a equivalent way of proceeding would be, instead of taking both sets of measurements by 4 and 4 'detectors mounted on an arm support 9 'ending in fork, to use the single detector 4 provided that it is mounted on the arm of support 9 by a coupling 40 allowing rotation (figure 2). The process would be exactly the same if only the two categories of signals would obtained successively.
  • detectors eddy currents such as detectors axisymmetric central coil emitting lines electromagnetic in all directions radiant, would only give results extremely imprecise in this app then an imprecision of standard deviation close to 10 ⁇ m for partitions a few millimeters thick can be hoped with the invention.

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  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
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Abstract

Method in which Eddy currents are applied using two poles of a detector (4) magnetic core. The currents applied are perpendicular to the wall (2) surface, i.e. parallel to support frames (3) behind the wall. The poles have coils connected in series with the wall thickness determined by displacement of the probe over the surface. The probe is pre-calibrated on a wall without supports and a software system is used to correct the results obtained for the effect of the sub-surface frames.

Description

Le sujet de cette invention est la mesure d'épaisseur d'une paroi d'une aube creuse.The subject of this invention is measurement thickness of a wall of a hollow blade.

Une caractéristique de ces pièces est qu'elles sont normalement munies de cloisons internes couvertes par la paroi, afin de raidir l'aube ou de compartimenter le volume interne. Ces cloisons perturbent les mesures puisque leurs contributions au signal de mesure se superposent à celles de la paroi et qu'elles tendent donc à être confondues avec des surépaisseurs. Il existe déjà plusieurs procédés non destructifs susceptibles d'accomplir des mesures d'épaisseur, mais certains, comme la tomographie aux rayons X où un réseau de détecteurs prend des vues successives autour de l'objet à reconnaítre, sont trop compliqués d'emploi alors que d'autres, comme les mesures aux infrarouges, sont trop peu précis. Enfin, les mesures aux ultrasons ne conviennent pas pour tous les matériaux, notamment ceux qui sont anisotropes.A feature of these pieces is that they are normally fitted with internal partitions covered by the wall, in order to stiffen the dawn or to compartmentalize the internal volume. These partitions disturb the measurements since their contributions to measurement signal overlap those of the wall and that they therefore tend to be confused with extra thickness. There are already several processes not destructive capable of performing measures thick, but some, such as X-rays where a network of detectors takes pictures successive around the object to be recognized, are too complicated to use while others, such as infrared measurements are too imprecise. Finally, ultrasonic measurements are not suitable for everyone materials, especially those that are anisotropic.

Un procédé particulier de mesures d'épaisseur non destructif et exempt de ces défauts a été développé pour donner des indications précises et fiables sur l'épaisseur d'une paroi malgré la présence de cloisons derrière cette paroi, à des emplacements mal connus et qui perturbent les mesures d'épaisseur.A particular measurement process of non-destructive thickness and free of these defects a been developed to give precise indications and reliable on the thickness of a wall despite the presence partitions behind this wall, at locations poorly known and which disturb thickness measurements.

Le procédé repose sur l'emploi d'un détecteur particulier de courants de Foucault, qui est conçu et employé pour que la contribution des cloisons au signal recueilli soit minimisée, et des moyens de traitement sont proposés pour éliminer substantiellement l'influence des cloisons sur la mesure. Plusieurs modes de réalisation particuliers sont possibles, plus ou moins raffinés et qui donnent des résultats précis en conséquence.The process is based on the use of a particular eddy current detector, which is designed and used so that the contribution of partitions to the signal collected is minimized, and means of treatment are offered to eliminate substantially the influence of partitions on the measured. Several specific embodiments are possible, more or less refined and which give accurate results accordingly.

Sous sa forme la plus générale, l'invention concerne un procédé de mesure d'épaisseur d'une paroi d'aube creuse susceptible de couvrir des cloisons, caractérisé en ce qu'il consiste à appliquer deux pôles d'un noyau magnétique d'un détecteur de courants de Foucault sur la paroi en alignement parallèle aux cloisons, les pôles (8) étant munies de bobines (7) reliées entre elles en série, à déplacer le détecteur sur la paroi perpendiculairement aux cloisons, à enregistrer un signal produit par le détecteur, et à en déduire l'épaisseur de la paroi d'après des étalonnages préliminaires.In its most general form, the invention relates to a method for measuring the thickness of a wall hollow blade capable of covering partitions, characterized in that it consists in applying two poles of a magnetic core of a current detector Eddy on the wall in alignment parallel to partitions, the poles (8) being provided with coils (7) connected together in series, to move the detector on the wall perpendicular to the partitions, at record a signal produced by the detector, and deduce the wall thickness from calibrations preliminary.

Le document US 4 005 359 A décrit une sonde à courants de Foucault appliquée à estimer l'épaisseur d'un revêtement de peinture ou d'émail sur un substrat conducteur ; elle se compose de deux bobinages disposés en transformateur, c'est-à-dire associés par induction électromagnétique mais non liés électriquement.Document US 4,005,359 A describes a probe eddy current applied to estimate thickness a coating of paint or enamel on a substrate driver; it consists of two windings arranged into transformer, i.e. associated by induction electromagnetic but not electrically linked.

Le document US 5 172 059 A montre qu'une bobine induisant des courants de Foucault dans un substrat sous elle est sensible à des variations d'épaisseur de ce substrat.Document US 5 172 059 A shows that a coil inducing eddy currents in a substrate under it is sensitive to variations thickness of this substrate.

L'invention sera décrite en détail au moyen des figures suivantes, qui feront mieux apparaítre ses caractéristiques, aspects et avantages, dans des modes de réalisation illustratifs :

  • la figure 1 est une vue générale du procédé ;
  • la figure 2 illustre en gros plan le détecteur ;
  • la figure 3 est une représentation d'un détecteur composite ;
  • la figure 4 est un exemple de signaux obtenus ;
  • la figure 5 illustre un réseau de neurones artificiels ;
  • et la figure 6 est une vue d'une cale d'étalonnage.
The invention will be described in detail by means of the following figures, which will better show its characteristics, aspects and advantages, in illustrative embodiments:
  • Figure 1 is a general view of the process;
  • Figure 2 illustrates the detector in close-up;
  • Figure 3 is a representation of a composite detector;
  • FIG. 4 is an example of signals obtained;
  • FIG. 5 illustrates a network of artificial neurons;
  • and Figure 6 is a view of a calibration block.

La figure 1 représente partiellement une aube 1 creuse dont le profil est dessiné par une paroi extérieure 2 raidie par des cloisons 3 de largeurs, de profondeurs et d'écartements différents et mal connus. Un capteur 4 est déplacé le long d'une génératrice 5 de l'aube 1. Il comprend un noyau magnétique 6 en arceau, sur lequel est formé un bobinage électromagnétique, ici composé de deux bobines 7 reliées entre elles en série et placées sur les branches 8 de l'arceau 6. Le détecteur 4 est au bout d'un bras de support 9 repoussé par un ressort 10 de manière que les bouts des branches 8 touchent la paroi 2 ; un appareil 11 à moteur permet de déplacer le bras 9 et le détecteur 4 le long de la génératrice 5. Un générateur de courant alternatif 12 est placé sur un circuit électrique 13 auquel les bobines 7 sont branchées en série, et un voltmètre 14 permet d'enregistrer la tension produite aux bornes des bobines 7 et de la transmettre à un moyen de traitement 15 qui constitue un élément important de l'invention. Le signal mesuré par le voltmètre 14 dépend en particulier des courants de Foucault que l'induction électromagnétique des bobines 7 produit sur la portion avoisinante de l'aube 1, et qui dépend, outre de l'épaisseur de la paroi 22, de la présence ou de l'absence d'une cloison 3 devant le détecteur 4 ou à proximité. On a toutefois découvert que, si les pôles du noyau 6, situés au bout des branches 8, étaient alignés dans la direction des cloisons 3, comme on l'a représenté, l'influence des cloisons 3 était beaucoup moins sensible sur la sonde présente, c'est-à-dire que le signal ne variait que faiblement quand le détecteur 4 passait devant une des cloisons 3. La figure 4 donne l'allure de la courbe obtenue (R1 pour une fréquence d'excitation de 100 kHz et R2 pour 300 kHz) pour un profil d'aube 1 figuré en regard.Figure 1 partially shows a 1 hollow blade whose profile is drawn by a wall exterior 2 stiffened by partitions 3 of widths, of different and poorly known depths and gaps. A sensor 4 is moved along a generator 5 of dawn 1. It comprises a magnetic core 6 in a hoop, on which an electromagnetic coil is formed, here composed of two coils 7 connected together in series and placed on the branches 8 of the hoop 6. The detector 4 is at the end of a support arm 9 pushed back by a spring 10 so that the ends of the branches 8 touch the wall 2; a motorized device 11 allows to move the arm 9 and the detector 4 along the generator 5. An alternating current generator 12 is placed on an electrical circuit 13 to which the coils 7 are connected in series, and a voltmeter 14 saves the voltage produced across the coils 7 and transmit it to a processing means 15 which constitutes an important element of the invention. The signal measured by the voltmeter 14 depends in particular of the eddy currents that induction electromagnetic coil 7 produced on the portion near dawn 1, and which depends, in addition to the thickness of the wall 22, the presence or the absence of a partition 3 in front of the detector 4 or at proximity. However, it was discovered that if the poles of the core 6, located at the end of the branches 8, were aligned in the direction of partitions 3, as we have depicted, the influence of partitions 3 was much less sensitive on the probe present, that is to say that the signal varied only slightly when the detector 4 passed in front of one of the partitions 3. Figure 4 gives the shape of the curve obtained (R1 for a frequency excitation of 100 kHz and R2 for 300 kHz) for a blade profile 1 shown opposite.

Si la tension mesurée par le voltmètre 14 est VB et l'intensité du courant passant par les bobines 7 est I, on peut écrire Z0 = V0 / I0 = R0 + jX0 où Z0 est l'impédance, R0 la résistance et X0 la réactance du circuit à l'état à vide (quand l'aube 1 est absente), et Zc = Vc / Ic = Rc + jXc quand le détecteur 4 est appliqué sur l'aube 1 ; j est la constante imaginaire (j2=-1). Le moyen de traitement peut exploiter les mesures notamment en relevant l'allure de la réactance normalisée Xcm = Xc / X0, ce qu'on propose ici, ou éventuellement de la résistance normalisée Rc - R0 / X0. On voit que pour des fréquences d'induction relativement faible, l'influence des cloisons 3 devient presque imperceptible, si bien qu'on peut même concevoir d'ignorer complètement leur existence et de déduire directement l'épaisseur de la paroi 2 d'après le signal capté, après un étalonnage préalable mené sur une série de parois lisses d'épaisseur différente.If the voltage measured by the voltmeter 14 is V B and the intensity of the current passing through the coils 7 is I, we can write Z 0 = V 0 / I 0 = R 0 + jX 0 where Z 0 is the impedance, R 0 the resistance and X 0 the reactance of the circuit in the no-load state (when the blade 1 is absent), and Z c = V c / I c = R c + jX c when the detector 4 is applied to l 'dawn 1; j is the imaginary constant (j 2 = -1). The processing means can use the measurements in particular by recording the appearance of the standardized reactance X cm = X c / X 0 , which is proposed here, or possibly of the standardized resistance R c - R 0 / X 0 . We see that for relatively low induction frequencies, the influence of partitions 3 becomes almost imperceptible, so that we can even conceive of completely ignoring their existence and directly deducing the thickness of wall 2 from the signal received, after a preliminary calibration carried out on a series of smooth walls of different thickness.

Il est toutefois préféré de recourir à des traitements plus compliqués pour déduire l'épaisseur de la paroi 2 du signal obtenu, et le moyen de traitement 15 où ces opérations sont entreprises mérite d'être décrit de façon plus détaillée. Il renferme un réseau de neurones artificiels pouvant prendre la disposition indiquée sur la figure 5. Un neurone artificiel N est en pratique un processeur élémentaire qui reçoit un certain nombre d'entrées e auxquelles sont associés des poids W, et fournit une sortie s qui dépend des entrées pondérées et de biais b, selon la formule s=F(We+b) où F est une fonction d'activation déterminée par la programmation du neurone N. Les données d'entrée circulent dans le réseau en étant modifiées à chaque neurone qu'elles traversent. Les neurones peuvent être répartis en couches successives et enchaínés à tous les neurones de la couche précédente et de la couche suivante. Dans le cas présent, on a constaté qu'un réseau à deux couches, comprenant une couche de sortie C2 à neurone unique fournissant la sortie souhaitée (l'épaisseur) et à couche inférieure ou cachée C1 composée de quelques neurones (deux, trois ou quatre en pratique) alimentés par les valeurs obtenues du signal (R1 ou R2 par exemple) était suffisant. De plus, les fonctions opérées par les neurones sont l'identité (F(W.e+b)=W.e+b) dans la couche C1 et la tangente hyperbolique (F(W.e+b)=tanh(W.e+b)) dans la couche C2. Le réseau de neurones subit un apprentissage préalable qui lui permet ensuite d'exprimer les paramètres descriptifs d'une nouvelle situation, ressemblant à la situation d'apprentissage, en fonction des signaux qu'il reçoit. On propose ici de faire un étalonnage au moyen d'une cale plane 30 (figure 6) formée de bandes parallèles 31 d'épaisseur croissante et munie de nervures 32, analogues aux cloisons 3, derrière cette plaque, à des intervalles différents, éventuellement d'épaisseurs et de largeurs différentes et qui coupent toutes les bandes 31. Le détecteur 4 est promené le long de ces bandes 31 de la même façon que pour l'aube 1, afin qu'il fournisse un nombre suffisant de signaux de référence qui sont exploités pour régler le réseau de neurones en ajustant les poids et les biais de ceux-ci. De tels apprentissages du réseau de neurones peuvent être faits automatiquement par des logiciels de façon que le réseau donne en sortie l'épaisseur connue de chaque bande 31 en fonction des signaux captés en parcourant cette bande.It is however preferred to use more complicated processing operations to deduce the thickness of the wall 2 from the signal obtained, and the processing means 15 where these operations are carried out deserves to be described in more detail. It contains a network of artificial neurons which can take the arrangement indicated in FIG. 5. An artificial neuron N is in practice an elementary processor which receives a certain number of inputs e with which weights are associated W, and provides an output s which depends weighted and biased inputs b, according to the formula s = F (We + b) where F is an activation function determined by the programming of neuron N. The input data circulates in the network being modified with each neuron that they cross. The neurons can be divided into successive layers and linked to all the neurons of the previous layer and the next layer. In the present case, it has been found that a two-layer network, comprising an output layer C 2 with a single neuron providing the desired output (the thickness) and with a lower or hidden layer C 1 composed of a few neurons (two, three or four in practice) supplied by the values obtained from the signal (R 1 or R 2 for example) was sufficient. In addition, the functions performed by the neurons are the identity (F (W.e + b) = W.e + b) in the layer C 1 and the hyperbolic tangent (F (W.e + b) = tanh ( W.e + b)) in layer C 2 . The neural network undergoes a prior learning which then allows it to express the descriptive parameters of a new situation, resembling the learning situation, according to the signals it receives. It is proposed here to make a calibration by means of a flat shim 30 (FIG. 6) formed of parallel strips 31 of increasing thickness and provided with ribs 32, similar to partitions 3, behind this plate, at different intervals, possibly d 'different thicknesses and widths which cut all the bands 31. The detector 4 is walked along these bands 31 in the same way as for blade 1, so that it provides a sufficient number of reference signals which are exploited to regulate the neural network by adjusting the weights and their biases. Such learning of the neural network can be done automatically by software so that the network outputs the known thickness of each band 31 as a function of the signals picked up by traversing this band.

Quoique l'agencement déjà décrit du détecteur 4 soit le préféré, les mesures peuvent être complétées par un détecteur 4' semblable, mais disposé avec les pôles alignés perpendiculairement aux cloisons 3 (figure 3), ce qui donne des lignes d'aimantation perpendiculaires à ces cloisons et des courants de Foucault importants en elles. Il est alors évident que l'influence des cloisons sera beaucoup plus forte sur les mesures qu'avec le détecteur 4, ce qu'on peut vérifier sur les courbes de réponse R3 et R4 de la figure 4. Les signaux du détecteur 4' fournis au réseau de neurones avec ceux du détecteur 4 permettent de corriger l'influence des cloisons et d'obtenir une précision encore meilleure pour l'évaluation de l'épaisseur de la paroi 2, puisque l'influence des cloisons 3 est mieux perçue par le détecteur 4'. Une façon équivalente de procéder aux mesures consisterait, au lieu de prendre simultanément les deux séries de mesures par des détecteurs 4 et 4' montés sur un bras de support 9' se terminant en fourche, à utiliser le seul détecteur 4 à condition de le monter au bras de support 9 par un accouplement 40 permettant la rotation (figure 2). Le procédé serait exactement semblable si ce n'est que les deux catégories de signaux seraient obtenues successivement.Although the arrangement already described of the detector 4 is preferred, measurements can be supplemented by a similar but arranged 4 'detector with the poles aligned perpendicular to the partitions 3 (Figure 3), which gives lines of magnetization perpendicular to these partitions and currents of Significant eddy in them. It is then obvious that the influence of the partitions will be much stronger on measurements with detector 4, which we can check on the response curves R3 and R4 of the figure 4. The signals from the 4 'detector supplied to the network of neurons with those of detector 4 allow correct the influence of the partitions and get a even better accuracy for assessing the thickness of wall 2, since the influence of partitions 3 is better perceived by the detector 4 '. A equivalent way of proceeding would be, instead of taking both sets of measurements by 4 and 4 'detectors mounted on an arm support 9 'ending in fork, to use the single detector 4 provided that it is mounted on the arm of support 9 by a coupling 40 allowing rotation (figure 2). The process would be exactly the same if only the two categories of signals would obtained successively.

Une autre source de perturbation provient de l'inclinaison du détecteur 4 ou 4', qui reste dans l'alignement du bras de support 9, sur l'aube 3 à cause de sa courbure. Toutefois, une correction peut être entreprise facilement puisqu'on peut vérifier que l'inclinaison n'a d'effet que sur les proportions des parties réelle et imaginaire du signal fourni par le voltmètre 14. Plus précisément, on peut écrire que Xcn=aRcn+b, où a est un coefficient qui dépend de l'inclinaison du détecteur 4 sur l'aube 1. Il suffit alors d'appliquer les signaux reçus à un réseau de neurones supplémentaire pour qu'il donne en sortie le signal rectifié, qui est celui qu'on aurait obtenu avec un détecteur 4 ou 4' orienté bien droit sur la paroi 2. Un apprentissage du réseau de neurones supplémentaire est obtenu en promenant le détecteur 4 sur les bandes 31 avec des inclinaisons différentes, pour déterminer des valeurs du coefficient a.Another source of disturbance comes from the inclination of the detector 4 or 4 ', which remains in the alignment of the support arm 9, on the blade 3 because of its curvature. However, a correction may be business easily since we can verify that the tilt only has an effect on the proportions of real and imaginary parts of the signal provided by the voltmeter 14. More precisely, we can write that Xcn = aRcn + b, where a is a coefficient which depends on the inclination of the detector 4 on the blade 1. It suffices then apply the received signals to a network of additional neurons so that it outputs the rectified signal, which is what we would have obtained with a detector 4 or 4 'oriented straight on the wall 2. Additional neural network learning is obtained by walking detector 4 on the bands 31 with different inclinations, to determine values of the coefficient a.

Il faut souligner que d'autres détecteurs de courants de Foucault, tels que des détecteurs axisymétriques à bobine centrale émettant des lignes électromagnétiques dans toutes les directions rayonnantes, ne donneraient que des résultats extrêmement imprécis dans cette application, alors qu'une imprécision d'écart-type proche de 10 µm pour des cloisons de quelques millimètres d'épaisseur peut être espérée avec l'invention.It should be noted that other detectors eddy currents, such as detectors axisymmetric central coil emitting lines electromagnetic in all directions radiant, would only give results extremely imprecise in this app then an imprecision of standard deviation close to 10 µm for partitions a few millimeters thick can be hoped with the invention.

Claims (5)

Procédé de mesure d'épaisseur d'une paroi d'aube (2) creuse susceptible de couvrir des cloisons (3), caractérisé en ce qu'il consiste à appliquer deux pôles (8) d'un noyau magnétique (6) d'un détecteur (4) de courants de Foucault sur la paroi en alignement parallèle aux cloisons, les pôles (8) étant munies de bobines (7) reliées entre elles en série, à déplacer le détecteur sur la paroi perpendiculairement aux cloisons, à enregistrer un signal produit par le détecteur, et à en déduire l'épaisseur de la paroi d'après des étalonnages préliminaires.Method for measuring the thickness of a hollow blade wall (2) capable of covering partitions (3), characterized in that it consists in applying two poles (8) of a magnetic core (6) of an eddy current detector (4) on the wall in alignment parallel to the partitions, the poles (8) being provided with coils (7) connected together in series, to move the detector on the wall perpendicular to the partitions, to record a signal produced by the detector, and to deduce the thickness of the wall from preliminary calibrations. Procédé de mesure selon la revendication 1, caractérisé en ce que les étalonnages préliminaires comprennent des séries de mesures sur des parois de référence (31) d'épaisseurs différentes et couvrant chacune des cloisons (32) séparées par des intervalles différents.Measuring method according to claim 1, characterized in that the preliminary calibrations comprise series of measurements on reference walls (31) of different thicknesses and covering each of the partitions (32) separated by different intervals. Procédé de mesure selon la revendication 1 ou 2, caractérisé en ce qu'il comprend un apprentissage d'un réseau de neurones (N) au moyen des étalonnages préliminaires, et en ce que l'épaisseur de la paroi est obtenue en fournissant le signal produit par le détecteur à une entrée du réseau de neurones.Measuring method according to claim 1 or 2, characterized in that it comprises learning a neural network (N) by means of preliminary calibrations, and in that the thickness of the wall is obtained by supplying the signal produced by the detector at an input to the neural network. Procédé de mesure selon l'une quelconque des revendications 1 à 3, caractérisé en ce qu'il consiste encore à appliquer deux pôles d'un noyau magnétique d'un détecteur de courants de Foucault (4') sur la paroi en alignement perpendiculaire aux cloisons, à déplacer le détecteur sur la paroi perpendiculairement aux cloisons, à enregistrer un second signal, produit par le détecteur, et en ce que l'épaisseur de la paroi est déduite des étalonnages préliminaires et, à la fois, du premier signal et du deuxième signal.Measuring method according to any one of Claims 1 to 3, characterized in that it also consists in applying two poles of a magnetic core of an eddy current detector (4 ') to the wall in alignment perpendicular to the partitions, to move the detector on the wall perpendicular to the partitions, to record a second signal, produced by the detector, and in that the thickness of the wall is deduced from the preliminary calibrations and, at the same time, from the first signal and the second signal. Procédé de mesure selon l'une quelconque de revendication 1 à 4, caractérisé en ce qu'il comprend une estimation d'inclinaison du détecteur sur la paroi et une correction de traitement de la déduction d'épaisseur en fonction de l'inclinaison.Measuring method according to any one of Claims 1 to 4, characterized in that it comprises an estimate of the inclination of the detector on the wall and a correction for processing the thickness deduction as a function of the inclination.
EP01401719A 2000-06-29 2001-06-28 Method for wall thickness measurement of a hollow blade Withdrawn EP1167917A1 (en)

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FR0008368 2000-06-29
FR0008368A FR2811076B1 (en) 2000-06-29 2000-06-29 METHOD FOR MEASURING THE WALL THICKNESS OF A HOLLOW BLADE

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WO (1) WO2002001145A1 (en)

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CA2381864C (en) 2010-06-01
JP4314029B2 (en) 2009-08-12
FR2811076B1 (en) 2002-09-20
FR2811076A1 (en) 2002-01-04
WO2002001145A1 (en) 2002-01-03
UA73948C2 (en) 2005-10-17
US6806703B2 (en) 2004-10-19
JP2004502152A (en) 2004-01-22
US20030184287A1 (en) 2003-10-02
RU2263878C2 (en) 2005-11-10

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